tnemelckram wrote:...
I think Hood was even worse. I base this on the fact that she blew up exactly like all the admirals and experts said she would and just like the three British battle cruisers at Jutland. It is hard to say that Bismarck's fatal hit was just lucky under these circumstances. Most people who knew Hood said that it was highly likely that this exact same hit would happen. There's no luck involved when the obvious happens.

This seams a bit odd to me. From what I've heard of the British inquest into the loss of the Hood there weren't any obvious explanations for what happened to her. It almost certainly wasn't what happened to the British BC's at Jutland. The main cause of that was identified and corrected.

JtD wrote:.....
The Hoods nominal armor layout was immune to the 38cm guns at the range the fatal hit occured. Neither the main belt nor the decks would be pierced by the German shell. So the shell found a weak spot, which existed. That's why I consider it a lucky hit.
(deck penetration of the German 38 cm shell at that range was about 3" of homogenous armor)

I must disagree here. The Hood was completely naked. The belt penetration of the German 38cm/52 is lethal at those ranges. Even the PoW's belt wasn't up to the task once broadside on. The Hood's deck armour was not armour grade material in the modern sense. The Krupp penetration curves for deck penetration of the 38cm are based on Wh, a thoroughly modern Chromium/Molybedenum armour grade alloy . The penetration would have been quite a bit greater against lesser materials. Moreover, the Hood's armour scheme didn't de-cap or create other effects ameliorating deck hits like the Bismarck's scheme did.

The Bismarck had a significant armour advantage at DS due to its armour scheme of backing up its belt with heavy scarps. Even if the Holland had stayed out there at relatively long range the Bismarck's armour pretection could have dealt effectively with possible deck hits in my opinion.

If Hood's belt had been presented at the normal, Bismarck's shells would have penetrated the belt, but as the angle of advance (0557 to 0600) caused the shells to come in at about 50 degrees from the bow, the belt was effectively much stronger in relation to incoming fire. Nathan Okun's article in Warship International N0. 4. 1978, gives a factor of 1.6 times normal thickness at 40 degrees, making Hood's belt behave as if it was 19 inches thick. Penetration of the belt would therefore seem very unlikely as the cause of Hood's destruction.

As the Hood adjusts course to unmask its aft guns the target angle changes. From the Krupp curves even at total obliquities exceeding 40* the penetration exceeds 13". Another way to look at it, at those ranges the penetration is 19-21". Moreover, German live fire tests were the test plates were angled to simulate sloped belts, the L4.4 AP shell still penetrated intact 308mm out to 25km.

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

Dave Saxton wrote:As the Hood adjusts course to unmask its aft guns the target angle changes. From the Krupp curves even at total obliquities exceeding 40* the penetration exceeds 13". Another way to look at it, at those ranges the penetration is 19-21". Moreover, German live fire tests were the test plates were angled to simulate sloped belts, the L4.4 AP shell still penetrated intact 308mm out to 25km.

Interesting. Do you have any opinion about why people like Nathan and Bill Jurens assumed in their various approaches to how Hood could have blown up the assumption that the belt itself couldn't have been penetrated? Obviously if the main belt is penetrated there is nothing to explain. The shell just blows up in the magazine and end of story. But all the experts have devised other theories, the main one being an explosion in the after engine room blowing up the 4" magazine and then the adjacent 15" magazine. Surely these people knew about the German tests; if you can look it up so can they, right?

I think part of the problem was that while a shell could get through main belt, it had several internal layers of protective plating and spaces to get through before reaching a magazine. In many instances, the shell might have been slowed up enough to detonate before reaching a magazine. The internal layers consisted of a relatively thin scarp and internal HT bulkheads around the magazine groups (if I recall correctly) together with several HT decks and the magazine crowns. An outright penetration of the main belt was certainly possible and a shell might well have made it far enough, but it is more likely that the shell struck forward of bulkhead between the after turbine room and the 4-inch HA magazine, and near the bottom of the 7-inch middle belt. If it had sufficient momentum and had come from slightly forward, it could have missed the internal layers of plating altogether and carried directly on into the magazine group.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

Dave Saxton wrote:
I must disagree here. The Hood was completely naked. The belt penetration of the German 38cm/52 is lethal at those ranges. Even the PoW's belt wasn't up to the task once broadside on. The Hood's deck armour was not armour grade material in the modern sense. The Krupp penetration curves for deck penetration of the 38cm are based on Wh, a thoroughly modern Chromium/Molybedenum armour grade alloy . The penetration would have been quite a bit greater against lesser materials. Moreover, the Hood's armour scheme didn't de-cap or create other effects ameliorating deck hits like the Bismarck's scheme did.

The Bismarck had a significant armour advantage at DS due to its armour scheme of backing up its belt with heavy scarps. Even if the Holland had stayed out there at relatively long range the Bismarck's armour pretection could have dealt effectively with possible deck hits in my opinion.

I've read Bill Jurens article, (http://www.navweaps.com/index_inro/INRO_Hood_p1.htm), thought it through and generally agree with his findings. With the angles that were there at the time of Hoods destruction, it was a lucky hit. Nominally, it's 3" of deck, plus 2" of deck, plus some " of inclined belt. Too much for the 38 cm shell at that distance.

Sure if you assume that those decks had a resistance to penetration eqivilent to that thickness of high quality homogonous armour.....

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

Well, they had. Compared to the German Wotan steels, the deck plates on the Hood offered about 90-95% the protection at the same thickness. I don't think there is a point in arguing 5% if the safety against penetration of the nominal armor is in the region of 100%.

For your info, we now know that Hood was turning when being destroyed, so neither the maximum nor the minimum angles Bill Jurens discussed apply.

I doubt that it was within 5% of Wh. British tests of Tirpitz Wh plates indicated that it took on average 10% more energy to penetrate the Wh than it did contemporary British homogenous armour. The Hood deck plates were only HT or High Tensile steel.

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

Wh (Wotan hart). Homogeneous armour steel with a tensile strength of 85-95 kg/mm², a strain of 20% and a yield point of 50-55 kg/mm². This material was used for the armoured decks, and, in the thickness employed aboard the Bismarck, was the equal of most foreign homogeneous plates.

85 kg/mm² translates to 833 MPa which is a bit less than the MPa for the lowest hardness 850-1500+ shown on the charts of my first reference.
Similarly the yield strength comes out to ~490 where that of the HT steel varies from 635-1125. At the very least "only HT" steel seams to not be much of a problem.

One also wonders how likely an AP shell in this case would be to penetrate the lower deck in any sort of shape. I would think given the obliquity that decapping would be a distinct possibility upon piercing the upper deck.

The modern "High Tensile Steel" listed in the link is not the same material as "HTS" of the Hood's era. Indeed 40xx series steels are a Cr/mo alloy and are a modern derivative Krupp Wotan steel. At the time of the Hood's construction 4030 series Cr/mo alloys hadn't been invented yet. The HTS of the interwar era is just a plain carbon steel with greater carbon content than mild steel.

The mechanical properties of steel alloys are set by the heat treatments they receive, and also by the cooling rates once heated. Heat treatments can be used to make steel harder and that also increases the utlimate tensile strength, but at the cost of reduced ductility. For example, Wh treated to a hardness of 225 brinell has a UTS of ~120,000 psi and an elongation of ~26%. Treated to a hardness of 255 brinell the UTS is increased to ~133,000 psi and the elongation is reduced to ~20%.

A good measure of toughness, or the ability to absorb kenetic energy before failure, is the ratio of ultimate tensile strength to yield strength. The YTS is the point were the material starts to deform, and the UTS is the point were it finally ruptures. The wider this ratio, then the greater the deformation capacity and toughness of the material under impact. In this metric Wh is about the best there is even by todays standards.

A regular HT carbon steel could be treated to to have similar tensile strength as a armour grade alloy, but the ductility ,toughness, and impact resistance, would compare very poorly. At a comparable ductility, a high tensile carbon steel would have a UTS of around 75,000 psi.

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

Dave Saxton wrote:The modern "High Tensile Steel" listed in the link is not the same material as "HTS" of the Hood's era. Indeed 40xx series steels are a Cr/mo alloy and are a modern derivative Krupp Wotan steel. At the time of the Hood's construction 4030 series Cr/mo alloys hadn't been invented yet. The HTS of the interwar era is just a plain carbon steel with greater carbon content than mild steel.

If I recall correctly the HT steel used in Hood's protective decks, torpedo bulkhead, and internal bulkheads around the magazines was a low content nickle steel. This was normally applied in 1-inch laminations to make up the desired total thickness. It was not, however, a ballistic armour quality steel, unlike STS and Wotan armours, and when tempered or work hardened, tended to become brittle when subjected to impacts. It was however good for minimizing the effects of blast or splinters from a shell.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

Dave Saxton wrote:I doubt that it was within 5% of Wh. British tests of Tirpitz Wh plates indicated that it took on average 10% more energy to penetrate the Wh than it did contemporary British homogenous armour. The Hood deck plates were only HT or High Tensile steel.

I don't think there is a point in arguing 10% if the safety against penetration of the nominal armor is in the region of 100%.

Well those tests comparing the Tirpitz Wh were compared to homogenous armour (NCA or noncemented armour) as would be worked into the decks of the more modern KGV class and not merely a HT steel. I think Tom has the most plausible explanation for the loss.

tommy303 wrote:......An outright penetration of the main belt was certainly possible and a shell might well have made it far enough, but it is more likely that the shell struck forward of bulkhead between the after turbine room and the 4-inch HA magazine, and near the bottom of the 7-inch middle belt. If it had sufficient momentum and had come from slightly forward, it could have missed the internal layers of plating altogether and carried directly on into the magazine group.

I don't believe that Hood had much of a IZ vs the German 38cm at any range except possibly at short range were the target angle was great.

Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.